Packaging container

ABSTRACT

In order to provide a packaging container having a beaker-shaped bottom part intended to hold package goods and provided with an upper edge defining the beaker opening, and having a lid for closing said beaker opening, preferably hermetically, said lid being preferably in the form of a ring-pull lid of metal, which packaging container is, in particular, a food-grade container of less weight than conventional containers but of the same quality with regard to the protection of the packaged goods, it is proposed that the bottom part is a deep-drawn plastics beaker which has an upper edge that is shaped during deep drawing and has a calibrated wall thickness and which forms a substantially no-play receiver for the lid.

[0001] The invention relates to a packaging container having a beaker-shaped bottom part to hold package goods, which bottom part has an upper edge defining a beaker opening and a lid which closes said beaker opening, preferably hermetically, and which is preferably in the form of a ring-pull lid of metal.

[0002] Such packaging containers are in use in diverse forms in the form of ring-pull cans for packaging food.

[0003] The beaker-shaped bottom part of these packaging containers is, as also the ring-pull lid itself, made of sheet zinc or sheet aluminum or aluminum foil and receives its shape by subjection to a deep-drawing process.

[0004] The energy balance of such packaging containers is relatively poor due to the necessity for steps for working metals to sheet metal, and, in addition, the packaging containers are of relatively high weight.

[0005] On the other hand, packaging containers of metal guarantee that the beaker-shaped bottom part and the lid member can be made to fit to each other In a precise manner, so that particularly sensitive packaged goods, such as foodstuffs, can be provided with guaranteed safe protection by reason of the excellent seal which can be achieved between the ring-pull lid and the beaker-shaped bottom part.

[0006] It is at object of the present invention to provide a packaging container of the same quality with regard to protection of the packaged goods, which is particularly suitable for containing foodstuffs and is less heavy.

[0007] This object is achieved according to the invention by a packaging container of the above type in which the bottom part is a deep-drawn plastics beaker which has a deep-drawn shaped upper edge of calibrated wall thickness and forms a substantially no-play receiver for the lid.

[0008] The lid is, in particular, a ring-pull lid, which makes it possible to open the packaging container without the assistance of tools.

[0009] In the present description of th invention a ring-pull lid is taken to mean any type of lid made of metal sheet and/or metal foil and frequently having an annular lid edge which can be sealingly connected to the upper edge of the bottom part and also has a frequently round middle area, which is separably connected to the lid edge. To the middle area there is fixed a handle in the form of a flap or ring, with the aid of which the middle area can be detached from the lid edge along a specified interface line and the package thus opened.

[0010] The beaker-shaped bottom parts are, of course, not limited to shapes exhibiting radial symmetry but can equally well have an oval or nearly rectangular beaker opening.

[0011] The upper edge of calibrated wall thickness provides the prerequisite for processing the packaging containers of the invention on existing packaging plants in the same way as prior art packaging containers having a metallic bottom part

[0012] Unlike metallic materials, plastics materials used for deep drawing must be heated, and this leads to problems concerning tolerances in the present usage. The outside diameter of the beaker-shaped bottom part and thus also the outside diameter of the edge surrounding the beaker opening is also preset by the deep-drawing die when deep drawing plastics sheets.

[0013] Deep drawing causes displacement of material leading to the formation of a bulge of accumulated material at the upper edge of the beaker-shaped bottom part, which cannot be controlled in conventional contrivances. Deep drawing of plastics sheets thus always involves a change in the wall thickness, particularly at the edge. As a result there are inadmissable variations in the size of the internal diameter, and in the thickness of the beaker edge, so that sealing problems arise when fixing the ring-pull lid.

[0014] An alternative method is to injection-mold the beaker, but this is inadmissable on account of the excessively high process costs involved.

[0015] The packaging container of the invention is thus only made possible by a process for the production thereof which is likewise subject matter of this invention and will be described in greater detail below, and in which the manufacturing process also involves calibration of the edge surrounding th beaker opening in a single step.

[0016] Preference is given to a beaker-shaped bottom part which is of plastics material and is stackabl . This allows for rational packaging of the goods to be packaged in the packaging containers.

[0017] In this context the side walls of the beaker-shaped bottom part are preferably slightly inclined outwardly. Another characteristic facilitating the separation of the stacked bottom parts is achieved by the provision of a projection in the region of the beaker edge on the inside thereof, which projection can, for example, run around the inside of the beaker at a given level so that the external surface of the succeeding beaker bears against the same. In this way the area of material contact between two successive beakers is reduced to a minimum, which decreases the risk of stacked beakers becoming jammed.

[0018] In another preferred embodiment, the beaker-shaped bottom part of the packaging container of the invention has a marginal area which widens radially outwardly from the side wall of the beaker.

[0019] Preferably, the projection intended as bearing surface for the outside wall of the succeeding beaker in the stack is disposed in this radially outwardly widened marginal area. Thus this structural solution still makes it possible to provide the material enclosing the effective volume of the beaker-shaped bottom part with smooth surfaces.

[0020] With regard to one of the preferred package goods for the packaging containers of the invention, namely food, it is an advantage when the beaker-shaped bottom parts of plastics material are sterilizable. Plastics materials satisfying such demands are known to the person skilled in the art. For example, polypropylene, high-density polyethylene, and crystalline polyesters are suitable.

[0021] Calibration of the thickness of the edge of the beaker-shaped bottom part of plastics material is preferably carried out with a tolerance of ±0.03 mm or less, particularly ±0.02 mm or less, based on a thickness of the edge of 0.4 mm. This permits secure closure with conventional ring-pull lids and, following sterilization of the sealed packaging container, guarantees maintenance of the sterility of the packaged goods over a long storage period.

[0022] A translucent or even transparent embodiment of th beaker-shaped bottom part is a particularly preferred goal, which is readily achieved with the solution of the invention. This is particularly advantageous when packaging foodstuffs, since the customers can be directly furnished with an optical impression of the packaged goods. Plastics sheets particularly well-suited for the production of translucent or transparent beaker-shaped bottom parts are, for example, polypropylene sheets. The portion of the beaker-shaped bottom part defining ist capacity is determined, in known manner, by the top ram.

[0023] The deep-drawing sheet is preheated in conventional manner before insertion into the deep-drawing die to a temperature just below its crystallite melting point, which in the case of polypropylene sheets is approximately 155° C.

[0024] In a preferred process, the depresser and the circumferential, downwardly extending ring-shaped projection for calibrating the thickness of the edge of the beaker-shaped bottom part are first of all moved down to their respective working positions, after which the deep-drawing sheet is shaped by the top ram to form a beaker-shaped bottom part.

[0025] Another preferred embodiment makes use of a depresser exhibiting, adjacent to the shoulder, a circumferential, downwardly extending, ring-shaped projection for calibrating the thickness of the edge of the beaker-shaped bottom part so that calibration and displacement of material are carried out at the edge of the beaker-shaped bottom part in a single process step together with clamping of the deep-drawing sheet in the deep-drawing die.

[0026] In a particularly preferred variant of the process of the invention, the circumferential, downwardly projecting projection provided for calibrating purposes is cooled during calibration and also during the deep-drawing operation itself.

[0027] These and other advantages of the invention are illustrated below in greater detail with reference to the drawings.

[0028] In the drawings:

[0029]FIG. 1 is a sectional view through a deep-draw contrivance for the production of the packaging container of the inv ntion and, for comparison, a deep-drawing contrivance illustrating th process of the prior art;

[0030]FIG. 2 is a detailed view of a contrivance for carrying out the process of the invention for the production of a packaging container of the invention;

[0031]FIG. 3 is a detailed view of a packaging container of the invention.

[0032]FIG. 1 shows on its right-hand side a conventional deep-drawing contrivance denoted by the general reference mark 10 and described below in detail. On the left-hand side of the drawing there is shown a novel deep-drawing contrivance 110 contain, with which the process of the invention can be carried out and a packaging container of the invention can be produced.

[0033] The two drawings in the left and right-hand halves of the figure are of a diagrammatic nature and are executed such that direct comparison can be made between conventional deep drawing and the process of the invention.

[0034] The conventional deep-drawing device 10 has a deep-drawing die 12 having a forming shoe 14, a depresser 16, a top ram 18, a blanking die 20, and a cutting punch 22.

[0035] The deep-drawing operation is started by placing a deep-drawing sheet 24 in the deep-drawing device 10 such that it can be fixed, when depresser 16 is depressed, in a position between an upper edge 26 of the forming shoe 14, which forms a seat, and the depresser 16 or its edge which completely surrounds the forming shoe 14 and the hollow mold present therein.

[0036] Then the top ram 18 is moved downwardly so as to deform the preheated sheet 24 and press it into the cavity of forming shoe 14 and thus form a beaker-shaped bottom part for a package.

[0037] Following shaping of the beaker-shaped bottom part, the remaining excess edge material of the deep-drawing sheet is then sh ared off by blanking plate 20, which is moved downwardly against cutting die 22 to cut out the beaker-shaped bottom part from the deep-drawing sheet. The top ram 18 is then moved upwardly and deep-drawing die 12 is opened by raising base plate 13, after which the resulting beaker-shaped bottom part is pressed out from shaping die 12 or forming shoe 14 by means of an ejector 28. The next deep-drawing operation can then take place, this again commencing with the insertion of the preheated deep-drawing sheet 24.

[0038] With this method, material accumulates in the region of the upper end of the side walls of the beaker-shaped bottom part near the upper edge 26 of forming shoe 14 forming a seat for the depresser, such accumulation of material being due to the displacement of material occurring during deep drawing by the action of top ram 18.

[0039] On account of the necessity to preheat the sheet, there is forced flow of the material of the deep-drawing sheet, this being a result which cannot be controlled to such an extent that the wall thickness in the region of the upper edge of the beaker-shaped bottom part to be formed can be produced with the required degree of precision. Whereas the outer contours of the beaker-shaped bottom part are defined by forming shoe 14 and here also a calibrated outside diameter can be obtained, the inside diameters of a beaker-shaped bottom part thus produced can deviate from each other when regarded following round the upper edge of the beaker-shaped bottom part. This forms a problem for the production of ring-pull packages, which are subjected to more stringent demands on the quality of the seal between the lid and the beaker-shaped bottom part.

[0040] Thus, as seen round the upper edge of the beaker-shaped bottom part, variations in the thickness of the material are produced which are contrary to the use of such conventionally produced beaker-shaped bottom parts for ring-pull packages.

[0041] By contrast, the deep-drawing device 110 according to the present invention has a deep-drawing die 112 which can be divided into an upper part, which is held in a base plate 113 for executing vertical up and down movements, and a lower part holding a forming shoe 114, in order to be able to place a preheated deep-drawing sheet 124 in the deep-drawing device when in this open position.

[0042] The upper part of the deep-drawing die is here again composed of a depresser 116 and an associated blanking die 120, similar to that previously described in detail for the conventional deep-drawing die 12.

[0043] The deep-drawing process of the invention also requires a cutting punch 122 for cooperation with blanking die 120 in order to make it possible to shear sheet residues from the beaker-shaped bottom part after the deep-drawing operation.

[0044] At the end of the operation an ejector 128 ejects the beaker-shaped bottom part out of the forming shoe 114 before a new deep-drawing operation can take place.

[0045] The deep-drawing device 110 of the invention differs from the conventional deep-drawing device 10 in that the region of depresser 116 and the upper edge of forming shoe 114 is differently designed, as is illustrated in greater detail in the enlarged-scale drawing shown in FIG. 2, which represents the detail X of FIG. 1 (mirrored). In particular, this again shows the fundamental structure of the deep-drawing device with its forming shoe 114, depresser 116, blanking die 120, and cutting punch 122.

[0046] The embodiment of the depresser 116 shown here has a circumferential shoulder 130, which is prestressed against a bearing surface 132 and clamps and fixes the deep-drawing sheet 124 (not shown) between itself and said bearing surface 132.

[0047] The preferred embodiment of the depresser 116 shown here exhibits a downwardly projecting circumferential projection 134 which adjoins the shoulder 130 radially inwardly thereof, and which, together with a wall surface extending radially inwardly from seat 132, forms and calibrates an upper edge of the beaker-shaped bottom part. Preferably, the projection 134 is cooled and forms, in the embodiment shown, a single unit with the shoulder of the depresser 116. The shoulder 130 of depresser 116 is inevitably also in a cooled state.

[0048] There is thus attained, in a simple manner, a very precisely defined and highly consistent edge thickness all round the edge (for example, an edge thickness of 0.4 mm ±0.02 mm), in that the deep-drawing die 112 is provided with a mechanical stop for the closing movement of the mold and, in particular, for the downward movement of the calibrating projection 134, this stop being here in the form of a nut 126 bearing against the base plate 113.

[0049] Alternatively, other forms of stop are, of course, suitable, such as bolts or downwardly projecting edges or the like, which require no further explanation for the person skilled in the art.

[0050] Frequently so-called multi-impression molds are used, by means of which, for example, 16 beaker-shaped bottom parts or beakers can be simultaneously formed. The aforementioned possibility of achieving narrow tolerances becomes particularly significant in the case of such multi-impression molds.

[0051] The result of such forming of a beaker-shaped bottom part of the invention is illustrated in FIG. 3, which will be described in detail below.

[0052] A peculiarity of the deep-drawing device illustrated in FIG. 2 is that in this case it is not the forming shoe 114 which forms the bearing surface for the deep-drawing sheet but rather forming shoe 114 ends with its inside wall flush against a recess 140 in cutting punch 122 below wall surface 136, which is responsible for shaping the marginal area at the perimeter of the beaker-shaped bottom part. The side wall 136 here is simultaneously part of cutting punch 122, as is also bearing surface 132. On account of the use of relatively large radii in the transition region between bearing surface 132 and side wall 136, on the one hand, and also in the transition region between shoulder 130 and projection 134 or its external side wall opposite side wall 136, on the other hand, it is possible to deform the deep-drawing sheet in a hot state and with a cooled projection 134 and to form a calibrated upper edge or an upper edge having a calibrated wall thickness without occurrence of material stress in the deep-drawing sheet in this region, which could impair the stability of the edge or the connection between the edge and the ring-pull lid (not shown).

[0053] The side wall 136, which is substantially vertical, is downwardly adjoined, toward the base of the beaker-shaped bottom part ie toward the bottom 142 of the beaker cavity of forming shoe 114, by another shoulder 144, which extends radially inwardly and which, in the closed state of the deep-drawing die as shown in FIG. 2, maintains an adequate distance to the top of projection 134 so that displacement of material can be readily absorbed in the space between projection 134 and shoulder 144. Since, in the region of shoulder 144, side wall 136 recedes from the inside wall of projection 134, there is free space at this point, which remains available even when the top ram (cf FIG. 1) is moved downwardly in order to deform the deep-drawing sheet to a beak r-shap d bottom part, so that displacement of material into this space is possible without leading to upsetting of the material and/or to stresses in the material, which could impair calibration of the thickness of the edge or calibration of the internal diameter of the beaker-shaped bottom part in the region of the edge defining the opening of the beaker-shaped bottom part. Stable geometry of the beaker edge is thus obtained which still remains when the beaker-shaped bottom part is ejected from deep-drawing die 112 by plunger 128 following the deep-drawing operation.

[0054] The base 142 of forming shoe 114 is connected to shoulder 144 by a vertically slightly inclined side wall 146, which makes it possible to form readily stackable beaker-shaped bottom parts of the invention.

[0055] Finally, FIG. 3 shows in detail the form of the top marginal area 150 and a beaker-shaped bottom part 152, shown only partially.

[0056] The upper marginal area 150 defines, as illustrated, the beaker opening and is subsequently closed when the packaging container is sealed with a (ring-pull) lid (not illustrated).

[0057] In order to acquire an optimum seal between the ring-pull lid and beaker 152, the edge 150 comprises an upper, substantially radially outwardly projecting flange 154 adjoined, via a curved portion, by a side wall 156 of calibrated thickness d. Adjoining the top edge 156 downwardly toward the base of the beaker the marginal area 150 exhibits a a bulge of accumulated material 158, which is caused by displacement of material occurring during calibration of the top edge 156.

[0058] The precise size of said bulge of material 158 is not, of course, relevant, as it is sufficient when the top edge 156 exhibits a calibrated thickness, which in turn provides a calibrated inside diameter of beaker 152, since the outside wall of the marginal area 150 is calibrated by the deep-drawing die (in the present case by wall 136 of cutting punch 122).

[0059] The bulge 158 also serves to prevent the beaker-shaped bottom parts 152 from touching each other at their bottoms when stacked so that separation of said bottom parts from each other for packaging purposes is very simply effected. 

1. A packaging container having a beaker-shaped bottom part intended to hold packag goods and having an upper edge defining a beaker opening and a lid which closes said beaker opening, characterized in that said bottom part is a deep-drawn plastics beaker having a top edge which is formed by deep drawing so as to have a calibrated wall thickness and which forms a substantially no-play receiver for the lid.
 2. A packaging container as defined in claim 1, characterized in that the beaker-shaped bottom part is of plastics material and is capable of being stacked.
 3. A packaging container as defined in claim 1 or claim 2, characterized in that the plastics beaker-shaped bottom part is made of a sterilizable plastics material.
 4. A packaging container as defined in any one of claims 1 to 3, characterized in that calibration of the wall thickness of the upper edge of the beaker-shaped bottom part guarantees a tolerance of ±0.03 mm or less, based on a thickness of the edge of 0.4 mm.
 5. A packaging container as defined in any one of claims 1 to 4, characterized in that the beaker-shaped bottom part is made of a translucent or transparent plastics material.
 6. A process for the production of a packaging container as defined in any one of claims 1 to 5, characterized in that a deep-drawable plastics sheet is deep-drawn by means of a deep-drawing die which comprises a top ram and a depresser exhibiting a circumferential shoulder which presses said deep-drawing sheet against a seat and fixes it in position during the deep-drawing operation, and the deep-drawing die further comprises a circumferential ring-shaped projection disposed radially inwardly of said shoulder and extending downwardly, which is moved beyond the shoulder of the depresser to project into the beaker space of the deep-drawing die, the wall thickness of the edge of the beak r-shaped bottom part being calibrated thereby to a specific thickness, whilst the beaker space of the bottom part is formed by the top ram in a manner known per se.
 7. A process as defined in claim 6, characterized in that said d press r and said ring-shaped, downwardly projecting projection are moved to their respective working positions for calibrating the thickness of the edge of said beaker-shaped bottom part, after which the top ram shapes the deep-drawing sheet to form said beaker-shaped bottom part.
 8. A process as defined in claim 7, characterized in that said depresser and said ring-shaped, downwardly projecting projection are moved together and simultaneously to their respective working positions.
 9. A process as defined in claim 8, characterized in that a depresser is used which forms a single unit with said downwardly projecting molded-on annular projection serving to determine the thickness of the edge of the beaker-shaped bottom part.
 10. A process as defined in any one of claims 6 to 9, characterized in that the ring-shaped, downwardly projecting projection provided for calibrating purposes is cooled. 